In commonly assigned U.S. Pat. Nos. 4,900,234, 4,907,414 and 5,005,376 a method and structure are disclosed for acoustic attenuation in hermetic compressors. Specifically, reduced radiated sound levels are achieved in low side hermetic compressors which are those in which all or most of the shell is filled with refrigerant at suction pressure. This sound reduction is achieved by diverting a small portion of the compressed refrigerant gas from the muffler and discharging the diverted gas through an orifice into the upper level of the oil in the sump. The method includes the steps of supplying pressurized refrigerant to a muffler, diverting a portion of the pressurized refrigerant supplied to the muffler and injecting the diverted pressurized refrigerant into the oil. This results in a supersaturated solution of refrigerant in oil in the upper level which drives the refrigerant out of the oil, thereby creating froth which provided sound reduction without disturbing the lower level which remains stratified. The fixed, continuous bleed provides sound attenuation without a significant efficiency loss in single speed compressors.
A fixed continuous high to low bleed orifice in a variable speed compressor adversely affects capacity and performance at low speed operation. This is because the leakage is not significantly reduced with a reduction in capacity and therefore the leakage is a higher percentage of the capacity. Additionally, the requirement for sound reduction is capacity related and is therefore normally not needed at low speed operation.